U.S. Pat. No. 8,508,238 B1 discloses an insertable polymer positive temperature coefficient (PPTC) over-current protection device that includes first and second electrodes 30; a solder material; conductive lead pins 50, 60 bonded to the first and second electrodes 30, respectively, and a PTC polymer matrix 20 laminated between the first and second electrodes 30 (see FIG. 1). The PTC polymer matrix 20 is formed with at least one hole 40 that has an effective volume to accommodate thermal expansion of the PTC polymer matrix 20 when the temperature of the PTC polymer matrix 20 is increased.
Electrical properties (e.g., operating current and high-voltage surge endurability) are important factors in the PPTC over-current protection device for preventing power surge. When the operating current of the PPTC over-current protection device is increased by increasing the thickness or the area of the PTC polymer matrix 20, it may become more vulnerable to power surge. On the other hand, when the high-voltage endurability of the PPTC over-current protection device is increased by decreasing the thickness or the area of the PTC polymer matrix 20, the PPTC over-current protection device is not necessarily less vulnerable to power surge.